This invention relates to improved filterability of the combustion products of a gas generating composition comprised of polyvinyl chloride and inorganic oxidizer salts. More particularly, it relates to a gas generating composition for use in the inflation of devices such as air bags, escape chutes, and life rafts. It is particularly directed to a method for improving the filterability of such gases during the inflation of air bags used in passenger vehicles to restrain the movement of passengers in the event of a crash.
Inflation of such devices is generally accomplished by the controlled decomposition of sodium azide or other azo compounds which releases large volumes of nitrogen gas, and by the release of a gas such as air, nitrogen, carbon dioxide, helium, argon, and the like from pressure vessels. Hybrid gas generators combine the stored gas and high temperature combustion product gases from the burning of gas generating compositions. U.S. Pat. Nos. 3,155,749; 3,723,205; and 4,981,534 (which are incorporated herein by reference) describe formulations for gas generating compositions which are used primarily in hybrid systems. Said formulations comprise a vinyl chloride polymer as the binder and fuel, a plasticizer, an oxidizer, a hydrogen chloride scavenger, a stabilizer for the polymer, a catalyst, and coolants. The hydrogen chloride scavenger is a halogen-free alkali metal salt. The alkali metal chlorides formed by the scavenging are extremely difficult to filter out of the combustion product gas before it enters the deploying air bag. At the combustion temperature of these compositions (on the order of 2800.degree. K. or about 2500.degree. C. and about 4600.degree. F.), the chlorides are all in the vapor phase. This fact essentially means that the filtration of such chlorides from the gas depends on the condensation of the vapors on the cold metal surfaces of the gas generator device.